Light emitting device

ABSTRACT

A light emitting device includes a light emitting element; a light reflecting member having an Ag-containing layer on a surface thereof; and a protective film having a thickness of 1 nm to 300 nm and covering a surface of the light reflecting member, the protective film covering a surface of the light reflecting member, in which the Ag-containing layer has a thickness of 0.1 μm to 0.5 μm.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/332,274, filed on Jul. 15, 2014, which claims priority to JapanesePatent Application No. 2013-148331, filed on Jul. 17, 2013, thedisclosures of which are hereby incorporated by reference in theirentireties.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present disclosure relates to a light emitting device including alight reflecting member having an Ag-containing layer.

2. Description of Related Art

In a light emitting device including a semiconductor light emittingelement (hereinafter, also referred to simply as a “light emittingelement”), various types of packages are employed in which silver (Ag)having a high reflectance to light from the light emitting element isprovided on the outermost surface. However, Ag reacts (is sulfurated)easily under an atmosphere where a sulfur-containing gas exists, andconsequently discoloration and corrosion occur, resulting in significantdeterioration of characteristics of the light emitting device, such as areduction in reflectance. Thus, attempts have been made with coveringthe surface of Ag with a protective film made from an inorganic materialsuch as glass or silica (e.g. JP 2007-324256 A and JP 2009-224536 A).

in thermal expansion coefficient between a member having Ag or a resinand the protective film. Discoloration and corrosion of Ag may easilyoccur due to ingress of a sulfur-containing gas from a portion where theprotective film is broken.

It is very difficult to fully cover Ag with a protective film, and gapssuch as pinholes may occur in the protective film. Discoloration andcorrosion of Ag may also occur from those portions that are not coveredwith the protective film.

SUMMARY

A light emitting device according to the present disclosure includes alight emitting element, a light reflecting member or a light reflectorhaving an Ag-containing layer on a surface thereof, and a protectivefilm having a thickness of 1 nm to 300 nm and covering a surface of thelight reflecting member, in which the Ag-containing layer has athickness of 0.1 μm to 0.5 μm.

According to the above-mentioned configuration, discoloration andcorrosion of Ag can be suppressed to provide a light emitting devicewhich is resistant to a reduction in reflectance and thus has highreliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a schematic plan view, and FIG. 1B shows a schematicsectional view, for explaining a light emitting device of oneembodiment.

FIG. 2 is a schematic enlarged sectional view for explaining aconfiguration of the light emitting device in FIG. 1.

FIGS. 3A-3D shows schematic sectional views for explaining an effect ofa light emitting device of one embodiment.

FIGS. 4A-4D show schematic sectional views of a light emitting device ofa comparative example for explaining an effect of a light emittingdevice of one embodiment.

FIG. 5 is a chart showing sulfuration test results for light emittingdevices of one embodiment of the present invention and light emittingdevices of comparative examples.

FIG. 6 is a chart showing sulfuration test results for light emittingdevices of one embodiment of the present invention and light emittingdevices of comparative examples.

DETAILED DESCRIPTION OF EMBODIMENT

An embodiment of the present invention will be described below withreference to the drawings. However, the embodiment shown below isintended to illustrate a light emitting device and a method forproducing the light emitting device for embodying the technical conceptof the present invention, and is not intended to limit the presentinvention to the following. Unless otherwise specified, the dimensions,materials, shapes, relative arrangements etc. of the componentsdescribed in the embodiment are not intended to limit the scope of thepresent invention thereto, but are merely illustrative. The sizes,positional relationships etc. of the members shown in the drawings maybe exaggerated for making explanations clear.

FIG. 1 shows a structure of a light emitting device 10 of thisembodiment. The light emitting device 10 of this embodiment includesthree light emitting elements 4 that are rectangular in a plan view, apair of flat plate-shaped light reflecting members 1 each having anAg-containing layer on a surface thereof, and a protective film 2 formedby an atomic layer deposition method, the protective film 2 coveringsurfaces of the light reflecting members 1, and the Ag-containing layerhas a thickness of 0.1 μm to 0.5 μm. More specifically, the lightemitting elements 4 are bonded onto one of the light reflecting members1 via a bonding member 5, and positive/negative electrodes provided onthe upper surfaces of the light emitting elements 4 and the pair oflight reflecting members 1 are each connected through two wires 7.Further, the light emitting device 10 includes a resin compact 3 that isapproximately square in a plan view with the light reflecting member 1partially embedded therein. The resin compact 3 has a recess portionthat is approximately circular in a plan view with the light reflectingmember 1 exposed at the bottom surface thereof. As shown in FIG. 1B, theprotective film 2 covers the surface of an Ag-containing layer 1 cexposed from the resin compact 3, the light emitting elements 4, thewires 7 and the surface of the resin compact 3. The light emittingdevice 10 has a sealing member 6 filled in the recess portion of theresin compact 3 so as to cover the protective film 2.

The components of the light emitting device of this embodiment will bedescribed in detail below.

Light Reflecting Member 1

The light reflecting member 1 is a member to reflect light from thelight emitting elements 4, has the Ag-containing layer 1 c on a surfacethereof, and is provided in the light emitting device 10 to reflectlight emitted from the light emitting elements 4 and/or thelater-described wavelength conversion member.

The light reflecting member 1 may be used in any appropriate form in thelight emitting device 10. For example, the light reflecting member 1 maybe provided below the light emitting elements 4 as in this embodiment,or may be provided in the form of a reflector surrounding the lightemitting elements 4. The light reflecting member 1 may be a lead frame,or may be wiring formed on a board. The light reflecting member 1 mayalso serve as a mounting member for mounting the light emitting elements4, a heat dissipation member for dissipating heat, and a conductivemember that is electrically connected to the light emitting element.Thus, the light reflecting member 1 preferably has good heatdissipation, good electrical conductivity and good wire bonding qualityaccording of the functions thereof.

In this embodiment, the light reflecting member 1 is formed in the shapeof a pair of flat plates that are approximately y rectangular in a planview as shown in FIGS. 1A and 1B. Further, the light reflecting member 1serves as a mounting member on which three light emitting elements 4 aremounted, and as positive/negative conductive members to which the lightemitting elements are each electrically connected through the two wires7.

The material of the light reflecting member 1 is not particularlylimited as long as the Ag-containing layer 1 c is provided on a surfacethereof, and the light reflecting member 1 may have a base member 1 a,an underlayer etc. as described below.

As shown in FIG. 2 which is an enlarged view of the part of FIG. 1Bencircled by broken line, the light reflecting member 1 of thisembodiment includes a first underlayer 1 b 1, a second underlayer 1 b 2,a third underlayer 1 b 3 and the Ag-containing layer 1 c in this order,around the base member 1 a, at the upper surface, the side surfaces andthe bottom surface.

Ag-Containing Layer 1 c

The Ag-containing layer 1 c is provided on a surface of the lightreflecting member 1, and has a thickness of 0.1 μm to 0.5 μm. When thethickness of the Ag-containing layer 1 c is less than 0.1 μm, the lightreflectance may be extremely reduced, so that the use of theAg-containing layer 1 c as a material of the surface of the lightreflecting member 1 becomes less advantageous. When the thickness ismore than 0.5 μm, sulfuration may easily proceed as described below, andtherefore such a thickness is not preferred.

The thickness of the Ag-containing layer 1 c is not particularly limitedas long as it is between 0.1 μm and 0.5 μm, but the thickness ispreferably 0.1 μm to 0.2 μm for preventing sulfuration. The thickness ofthe Ag-containing layer 1 c is preferably 0.3 μm to 0.5 μm forincreasing the light reflectance.

The surface of the Ag-containing layer 1 c or the light reflectingmember 1 preferably has a reflectance of 70% or more, especiallypreferably 80% or more to light having a wavelength in the visible lightregion. Light extraction efficiency can be thereby improved. TheAg-containing layer 1 c or the light reflecting member 1 preferably hashigh gloss, and the glossiness is preferably 0.5 or more, morepreferably 1.0 or more, further preferably 1.6 or more. The glossinessmentioned here is a value obtained when light is applied at 45° andvertically received using Micro Surface Color-Difference Meter VSR 300Amanufactured by NIPPON DENSHOKU INDUSTRIES Co., LTD.

As a material of the Ag-containing layer 1 c, Ag alone, or an alloy ofAg and Au, Pt, Rh, Pd, Os, Ru, Sn, In, Zn, Te or the like can be used.When the material is an Ag alloy, the ratio of silver is preferablyabout 70% to 99%.

The Ag-containing layer 1 c is not required to be provided on the wholesurface of the light reflecting member 1. That is, it suffices that atleast a part of the surface of the light reflecting member 1 is theAg-containing layer 1 c. For example, in the light reflecting member 1,a portion which is not exposed at the bottom surface of the recessportion of the substrate 3 shown in FIG. 1, i.e. an embedded portion 11embedded in the side wall portion of the resin compact 3, an externalterminal portion 12 exposed at the outside of the resin compact 3, and amounting portion 13 exposed on the bottom surface side of the lightemitting device may not have the Ag-containing layer 1 c on theirsurfaces. For providing the Ag-containing layer 1 c on a part of thelight reflecting member 1 as described above, a portion where theAg-containing layer is not formed can be protected with a mask using aresist or a protective tape when a film is formed.

Base Member 1 a

The light reflecting member 1 may include the base member 1 a inaddition to the Ag-containing layer 1 c for various purposes.

The base member 1 a is used as a material for determining a rough shapeof the light reflecting member 1.

As a material of the base member 1 a, Cu, Fe, an alloy thereof, a cladmaterial (e.g. a laminate of Cu/FeNi/Cu) etc. can be suitably used. Cuand alloys thereof have good heat dissipation, and therefore can besuitably used. Particularly, plate-shaped Cu and Cu alloys are preferredbecause they are also good in terms of mechanical characteristics,electric characteristics, processability and so on. The clad material ispreferred because a clad material has lower linear expansioncoefficient, so that the reliability of the light emitting device 10 isenhanced.

The thickness, shape etc. of the base member 1 a can be variouslyselected according to the shape etc. of the light emitting device 10.The base member 1 a can be in the shape of a plate, a block-like, a filmor the like. Further, the base member 1 a may be a wiring patternprovided on ceramic etc. by printing etc., or may be a material obtainedby plating the formed wiring pattern with Cu or an alloy thereof.

Underlayer 1 b

A layer of a different material can be provided below the Ag-containinglayer 1 c for various purposes.

It is preferred that a metal which hardly reacts with a sulfur componentas compared to Ag is used for the underlayer 1 b of the Ag-containinglayer. Specifically, Au, Au alloys, Pd, Pd alloys and so on arepreferred. Particularly, an Au layer is preferred. The progress ofsulfuration from below the Ag-containing layer can be suppressed, sothat sulfuration of the Ag-containing layer 1 c can be suppressed.

It is preferred that a diffusion prevention layer is provided as theunderlayer 1 b for preventing diffusion between the Ag-containing layer1 c and a layer provided therebelow. Particularly, when Cu is used forthe base member 1 a, it is preferred that Ni, Pd and Au are sequentiallystacked as the diffusion prevention layer. By employing such anarrangement, Cu in the base member 1 a can be suppressed from diffusinginto the Ag-containing layer 1 c to suppress deterioration of adhesionand quality of the bonding of the wire.

The underlayer 1 b may be a layer that plays a role in both ofsulfuration prevention and diffusion prevention. Costs can be therebyreduced. For example, Au can be suitably used as a layer providedimmediately below the Ag-containing layer 1 c because Au hardly reactswith a sulfur component and has high diffusion prevention effect.

It is preferred that layers such as the Ag-containing layer 1 c and theunderlayer 1 b are formed by plating. When the light reflecting memberhas the base member 1 a, it is preferred that the base member 1 a ispretreated before plating is performed. Examples of the pretreatmentinclude acid treatments with dilute sulfuric acid, dilute nitric acid,dilute hydrochloric acid and the like, and alkali treatments with sodiumhydroxide and the like. As the pretreatment, the same treatment or acombination of different treatments may be performed once or severaltimes. When the pretreatment is performed several times, it is preferredthat washing with flowing water is performed using pure water after eachtreatment. Dilute sulfuric acid is preferred when the base member 1 a isa metal plate composed of Cu or an alloy containing Cu, and dilutehydrochloric acid is preferred when the base member 1 a is a metal platecomposed of Fe or an alloy containing Fe.

When the Ag-containing layer 1 c is formed by electroplating, theglossiness can be improved by using a brightening agent such as aSe-based brightening agent, a Sb-based brightening agent, a S-basedbrightening agent or an organic brightening agent. When the brighteningagent is used in a large amount, components of the brightening agent maybe entrapped in the Ag-containing layer 1 c to cause deterioration ofcorrosion resistance. However, in this embodiment, the underlayer 1 b isformed before the Ag-containing layer 1 c is plated, and film qualitythereof is controlled, so that a high level of glossiness can beachieved even when the used amount of the brightening agent is reduced.The light reflecting member 1 having good corrosion resistance whilehaving a high glossiness can be thereby obtained.

The flatness of the base member 1 a is preferably as high as possiblefor increasing the light reflectance of the light reflecting member 1.For example, the surface roughness Ra is preferably 0.5 μm or less.Thereby, the flatness of the underlayer 1 b and the Ag-containing layer1 c provided on the base member 1 a can be increased, and as in thepresent embodiment where the Ag-containing layer 1 c that reflects lighthas a very small thickness of 0.1 μm to 0.5 μm, the light reflectance ofthe light reflecting member 1 can be satisfactorily increased. Theflatness of the base member 1 a can be increased by performing atreatment such as a rolling treatment or physical/chemical polishing.

Protective Film 2

The protective film 2 covers at least the Ag-containing layer 1 cprovided on a surface of the light reflecting member 1 so thatprincipally prevents discoloration and corrosion of the Ag-containinglayer 1 c on a surface of the light reflecting member 1. Further, theprotective film 2 may cover a surface of a member other than the lightreflecting member 1, such as the light emitting element 4, the bondingmember 5, the wire 7 or the substrate (resin compact 3), and a surfaceof the light reflecting member 1 which is not provided with theAg-containing layer 1 c.

In this embodiment, the protective film 2 is provided not only onsurfaces of the Ag-containing layer 1 c and the light reflecting member1 but also continuously on surfaces of the light emitting elements 4,the bonding member 5, the wires 7, the resin compact 3 etc. Theprotective film 2 of this embodiment is continuously formed oversurfaces of the members immediately after formation of the protectivefilm 2. However, with passage through the subsequent involvingtemperature rising and falling in the production process, e.g. a sealingmember forming step, cracks 2C may be generated at or near boundariesbetween members due to a difference in thermal expansion coefficientbetween the members, e.g. between the resin compact 3 and the lightreflecting member 1, between the bonding member 5 and the lightreflecting member 1, and between the wire 7 and the light reflectingmember 1.

The protective film 2 of the present embodiment is formed by using anatomic layer deposition (hereinafter, also referred to as ALD) method.According to the ALD method, a very uniform protective film 2 can beformed, and sulfuration of the Ag-containing layer 1 c can be veryeffectively prevented because the formed protective film 2 is denserthan protective films obtained by other film formation methods.

Unlike the sputtering method, the ALD method is a method in which atomiclayers of reaction components are formed one by one. Formation of theprotective film 2 of aluminum oxide (Al₂O₃) using TMA(trimethylaluminum) and H₂O will be described below.

First, a H₂O gas is introduced into a chamber to form OH groups on asurface of an object to be covered. Next, an excessive gas is exhausted,and a TMA (trimethylaluminum) gas is then introduced into the chamber toreact TMA with OH groups on the surface of the object to be covered withthe protective film 2 (first reaction). Next, a H₂O gas is introducedinto the chamber to react H₂O with TMA bound with OH groups (secondreaction). Next, an excessive gas is exhausted, and the first reactionand the second reaction are repeated to form a dense aluminum oxide filmhaving a desired thickness.

Examples of the material of the protective film 2 include, in additionto the above-mentioned Al₂O₃, oxides such as SiO₂, TiO₂, ZrO₂, ZnO,Nb₂O₅, MgO, In₂O₃, Ta₂O₅, HfO₂, SeO, Y₂O₃ and SnO₂, nitrides such asAlN, TiN and ZrN, and fluorides such as ZnF₂ and SrF₂. They may be usedalone, or mixed and used. Alternatively, they may be stacked on oneanother.

The thickness of the protective film 2 is preferably about 1 nm to 300nm, more preferably 5 nm to 100 nm although the preferred range somewhatvaries depending on a material to be used. When a plurality of layersare stacked, it is preferred that the total thickness of the layersfalls within the above-mentioned range.

It is preferred that the protective film 2 is formed after the wires 7are provided. Thereby, sulfuration of the Ag-containing layer 1 c aroundthe wires 7 and resulting breakage of the wires 7 can be effectivelyreduced.

The effect of reducing sulfuration can be obtained as long as theprotective film 2 covers at least a part of the surface of theAg-containing layer 1 c, but it is preferred that the protective film 2covers substantially the entire surface of the Ag-containing layer 1 cthat reflects light of the light emitting device 10. For example, in thecase where a recess portion is provided to house the light emittingelements 4 and the light reflecting member 1 is exposed at the bottomsurface of the recess portion as in the light emitting device 10 shownin FIG. 1, it is preferred that the protective film 2 coverssubstantially the entire surface of the Ag-containing layer 1 c exposedin the recess portion. Thereby, reliability of the light emitting device10 can be enhanced while light extraction efficiency thereof is improvedby the Ag-containing layer 1 c.

Advantageous effects obtained by the configuration of the presentembodiment will now be described.

FIGS. 3A through 3D and FIGS. 4A through 4D each show schematic views ofsulfuration of the Ag-containing layer 1 c covered with the protectivefilm 2 formed by using an atomic layer deposition method. FIGS. 3Athrough 3D show a case where, as in an embodiment, the Ag-containinglayer 1 c is thin. FIGS. 4A through 4D show a case, as a comparativeexample, where the Ag-containing layer 1 c is thick.

First, at a portion of the surface of the Ag-containing layer 1 c whichlacks the protective film 2 due to peeling between the resin compact 3and the light reflecting member 1, crack 2C etc. (generated near theboundary between the resin compact 3 and the light reflecting member 1)as shown in FIGS. 3A and 4A, the Ag-containing layer 1 c reacts with asulfur-containing gas shown by the arrow, such as S₈ or H₂S, whichinitiates sulfuration of the Ag-containing layer 1 c. As describedabove, the protective film 2 formed by using the atomic layer depositionmethod has a high effect of preventing sulfuration, and thereforesulfuration hardly occurs at a portion of the surface of theAg-containing layer 1 c where the protective film 2 is formed.

At this time, when the Ag-containing layer 1 c is very thin as in thepresent invention, sulfuration occurs relatively rapidly in thethickness direction from the surface of the Ag-containing layer 1 c,resulting in formation of silver sulfide 1 cS as shown in FIG. 3B. Inthis case, subsequent sulfuration proceeds in the lateral direction(plane direction) of the Ag-containing layer 1 c. Since the thickness ofthe Ag-containing layer 1 c is small, the area of a portion is verysmall where the Ag-containing layer 1 c and the sulfur-containing gascome into contact with each other to cause a sulfuration reaction(sulfuration reaction portion 1 cR). Thereby, the progression ofsulfuration can be considerably reduced. Accordingly, migration of Agions in the Ag-containing layer 1 c which is caused by formation ofsilver sulfide 1 cS decreases. Thus, cavitation of the Ag-containinglayer 1 c associated with migration of Ag ions, and expansion of thecontact area between the Ag-containing layer 1 c and thesulfur-containing gas due to ingress of the sulfur-containing gas into acavity portion 1 cH formed by the cavitation can be reduced (FIG. 3C).Thereby, the progression of sulfuration can be further reduced. Sincethe thickness of the Ag-containing layer 1 c itself is small, thethickness of silver sulfide 1 cS is also small, so that influences ofblackening are insignificant even if sulfuration proceeds.

For the reason described above, in the present invention, a reduction inreflectance due to sulfuration of the Ag-containing layer 1 c can beminimized.

On the other hand, when the Ag-containing layer 1 c is thick, thesulfuration reaction extensively proceeds in the thickness direction andplane direction of the Ag-containing layer 1 c as shown in FIG. 4B. Thisis because since the thickness of the Ag-containing layer 1 c is larger,the area of the Ag-containing layer 1 c which contacts/reacts with thesulfur-containing gas in the thickness direction increases, so thatsulfuration of Ag rapidly progresses. In addition, since the thicknessof the Ag-containing layer 1 c is large, Ag exists in a large amount, sothat Ag ions are abundantly supplied to the sulfuration reaction portion1 cR. Accordingly, sulfuration further proceeds. A large number ofcavity portions 1 cH are easily generated in the Ag-containing layer 1 cassociated with supply/migration of Ag ions, and sulfuration of Agfurther proceeds due to ingress of the sulfur-containing gas into thecavity portions 1 cH (FIGS. 4C and 4D). For the reason described above,sulfuration of the Ag-containing layer 1 c proceeds, leading to areduction in reflectance.

That is, as in the present invention, when the protective film 2 isformed by the atomic layer deposition method in order to make theprotective film 2 very dense, and the thickness of the Ag-containinglayer 1 c covered with the protective film 2 is 0.1 μm to 0.5 μm, thelight emitting device 10 having both a proper light reflectance andproper reliability can be provided.

Light Emitting Element 4

As the light emitting element 4, a semiconductor light emitting elementwith an appropriate wavelength can be selected. For example, for thelight emitting element 4 to emit blue and green light, a nitride-basedsemiconductor such as InGaN, GaN or AlGaN or one including GaP can beused. For the red light emitting element, GaAlAs, AlInGaP or the likecan be used. Further, the light emitting element 4 composed of amaterial other than those described above can also be used. Thecomposition, luminescent color, size, number, etc. of the light emittingelement 4 to be used can be appropriately selected according to apurpose.

When a light emitting device 10 having a wavelength conversion member isprovided, examples of the preferred light emitting element includenitride semiconductors capable of emitting light having a shortwavelength which enables the wavelength conversion member to beefficiently excited. A light emission wavelength can be variouslyselected according to a material of the semiconductor layer and a degreeof mixed crystal thereof. The light emitting element 4 that outputs notonly light in the visible light region but also ultraviolet rays andinfrared rays can be used.

It is preferred that the light emitting element 4 is mounted on thelight reflecting member 1. Light extraction efficiency of the lightemitting device 10 can be thereby improved.

The light emitting element 4 has positive/negative electrodeselectrically connected to the conductive member. These positive/negativeelectrodes may be provided on one surface side, or may be provided onboth upper and lower surfaces of the light emitting element 4. Themethod for connecting the electrodes to the conductive member is notparticularly limited, and they may be connected by the wires 7 to bedescribed below, or may be connected by flip-chip mounting.

As a member for fixing/mounting the light emitting element 4 on thelight emitting device 10, the bonding member 5 can be used. As apreferred material, a conductive paste of silver, gold, palladium or thelike, a eutectic solder material of Au—Sn, Sn—Ag—Cu or the like, abrazing material of a low-melting-point metal etc., a bond between thesame materials using Cu, Ag and Au particles or films, or the like canbe used for the conductive bonding member 5. For the insulating bondingmember 5, an epoxy resin composition, a silicone resin composition, apolyimide resin composition or a modified resin thereof, a hybrid resin,or the like can be used. When the above-mentioned resin is used, a metallayer having a high reflectance, such as an Al film or an Ag film, or adielectric reflective film can be provided on the mounting surface ofthe light emitting element 4 in consideration of degradation caused bylight and heat from the light emitting element 4.

It is preferred that the light emitting element 4 is mounted on theAg-containing layer 1 c of the light reflecting member 1 because lightextraction efficiency can be improved. In this case, cracks 2C may beformed in the protective film 2 on the periphery of the light emittingelement 4 due to a difference in thermal expansion coefficient betweenthe bonding member 5 and the light reflecting member 1, leading tosulfuration of the Ag-containing layer 1 c in the vicinity of the lightemitting element 4. However, by ensuring that the Ag-containing layer 1c has a very small thickness of 0.1 μm to 0.5 μm as in the presentinvention, the progression of sulfuration can be reduced and a reductionin light reflectance can be suppressed.

For supplying electricity to the light emitting element 4, anelectrically conductive bonding member 5 can be connected to theelectrode of the light emitting element 4, or alternatively the wire 7can be used. The wires 7 can also be provided to connect a plurality oflight emitting elements 4. As shown in FIG. 1A, each of the lightemitting elements 4 may be provided with a wires 7 to connect to therespective leads.

When the wire 7 is connected to the light reflecting member 1, it ispreferred that the protective film 2 is also provided on the surface ofthe wire 7. Thereby, disconnection between wire 7 and light reflectingmember 1 due to sulfuration can be prevented and reliability of thelight emitting device 10 can be enhanced. For the material of the wire7, Au, Al, Cu or the like is suitably used. Ag or an Ag alloy having ahigh light reflectance may be used. In this case, it is preferred thatthe protective film 2 is provided so as to cover the wire 7. Thereby,sulfuration and breakage of the Ag wire can be prevented to enhancereliability of the light emitting device 10.

Substrate 3

The light emitting device 10 of the present invention may have thesubstrate 3.

The substrate 3 is, for example, a member for supporting orholding/fixing the light reflecting member 1.

Resin Compact

The light emitting device 10 of this embodiment includes the resincompact 3 as the substrate 3. The resin compact 3 is a member having asa base a resin that integrally holds a pair of light reflecting members1. The shape of the substrate 3 in a plan view may be a substantiallyrectangular outer shape as shown in FIG. 1 as well as a shape such as aquadrangle, a polygon or a combination thereof. When the resin compactof the light emitting device 10 has a recess portion, the side wallportion of the recess portion is provided such that the inner surfacethereof is inclined with respect to the bottom surface as shown in FIG.1B. Alternatively, the inner surface may be substantially perpendicularto the bottom surface, or the side wall portion may have a stepdifference. The height thereof, the shape of the opening, etc. can beappropriately selected according to a purpose and a use. It is preferredthat the light reflecting member 1 is provided in the recess portion. Inthis embodiment, the light reflecting member is provided on the bottomsurface portion, but it may be provided on the side wall portion.

As the base of the resin compact 3, a thermosetting resin or athermoplastic resin can be used, and particularly a thermosetting resinis preferably used. The thermosetting resin is preferably a resin havinglower gas permeability as compared to a resin used for the sealingmember 6, and specific examples thereof may include an epoxy resincomposition, a silicone resin composition, a modified epoxy resincomposition such as a silicone-modified epoxy resin, a modified siliconeresin composition such as an epoxy-modified silicone resin, a polyimideresin composition, a modified polyimide resin composition, a urethaneresin and a modified urethane resin composition. Preferably, fineparticles etc. of TiO₂, SiO₂, Al₂O₃, MgO, MgCO₃, CaCO₃, Mg(OH)₂, Ca(OH)₂or the like are mixed as a filler in the base of the resin compact 3 toadjust the transmittance of light so that about 60% or more, morepreferably about 90% of light from the light emitting element can bereflected.

When the protective film 2 is formed after the light reflecting member 1is embedded in the resin compact 3, the protective film 2 is not formedon the surface of an embedded part (embedded portion 11). Thus, ifpeeling etc. occurs between the resin compact 3 and the light reflectingmember 1, the light reflecting member 1 which is not provided with theprotective film 2 may be in contact with the sulfur-containing gas.Thereby, the Ag-containing layer 1 c embedded in the resin compact 3 canbe sulfurated, and the Ag-containing layer 1 c at other portions can beprevented from being sulfurated.

The substrate 3 is not limited to the above-mentioned one having a resinas a base, and it may be formed of an inorganic substance such asceramic, glass or metal. Thereby, there can be provided the lightemitting device 10 which is hard to undergo degradation etc. and hashigh reliability.

Sealing Member 6

As shown in FIG. 1B, the light emitting device 10 of the presentinvention may include a sealing member 6. When the sealing member 6 isprovided so as to cover members such as the light emitting element 4,the light reflecting member 1, the protective film 2 and the wire 7, thecovered member can be protected from dust, moisture, external forcesetc., so that reliability of the light emitting device 10 can beenhanced. Particularly, it is preferred that the sealing member 6 isprovided on the protective film 2 after the protective film 2 is formedto protect the protective film 2, so that reliability of the lightemitting device 10 is enhanced.

The sealing member 6 may be provided in any appropriate shape. Thesealing member 6 may be provided so as to fill the inside of the recessportion of the resin compact 3 as in FIG. 1, or may be provided in theshape of a substantially hemispheric lens.

The sealing member 6 is preferably one having translucency allowingtransmission of light from the light emitting element 4 and having lightresistance such that the sealing member 6 is hardly degraded by thelight. Specific examples of the material may include insulating resincompositions having translucency allowing transmission of light from thelight emitting element, such as silicone resin compositions, modifiedsilicone resin compositions, modified epoxy resin compositions andfluororesin compositions. Particularly, a hybrid resin containing atleast one resin having a siloxane backbone as a base, such as dimethylsilicone, phenyl silicone having a low phenyl content, a fluorine-basedsilicone resin, or the like can also be preferably used.

The method for forming the sealing member 6 is not particularly limited.When the sealing member 6 is a resin, a potting (dropping) method, acompression molding method, a printing method, a transfer moldingmethod, a jet dispersing method, spray coating or the like can be used.In the case of the substrate 3 having a recess portion as in FIG. 1, apotting method is preferred, and when the flat plate-shaped substrate 3is used, a compression molding method and a transfer molding method arepreferred.

The shape of the outer surface of the sealing member 6 is notparticularly limited, and may be variously selected according to a lightdistribution characteristic required for the light emitting device 10.Also, for example, when the upper surface is convex lens-shaped, concavelens-shaped, Fresnel lens-shaped or roughened, directionalcharacteristics and light extraction efficiency can be adjusted.

A colorant, a light diffusing agent, a light reflecting material,various kinds of fillers, a wavelength conversion member and the likecan also be included in the sealing member 6.

The wavelength conversion member is a material that subjects light ofthe light emitting element 4 to wavelength conversion. When lightemitted from the light emitting element 4 is blue light, anyttrium-aluminum-garnet-based phosphor (hereinafter, referred to as“YAG:Ce”), a kind of aluminum oxide-based phosphors, is suitably used asthe wavelength conversion member. The YAG:Ce phosphor, depending on thecontent thereof, absorbs a part of light of blue color from the lightemitting element, and emits light of yellow color as a complementarycolor, so that a high-power light emitting device 10 that emits whitemixed-color light can be relatively easily formed.

The light emitting device 10 can include various members in addition tothose described above. For example, a Zener diode can be mounted as aprotective element 8.

EXAMPLES

A light emitting device having a structure substantially similar to thatof the light emitting device in FIG. 1 was produced as an example.Specifically, as a light reflecting member 1, a pair of lead frames 1were provided by sequentially forming, on a surface of a Cu base member1 a, Ni in a thickness of 1 μm, Pd in a thickness of 0.03 μm and Au in athickness of 0.005 μm as an underlayer, and an Ag-containing layerthereon by electroplating. Samples were provided with five differentthicknesses of the Ag-containing layer, which are selected within therange of 0.1 μm to 3.0 μm as shown in FIG. 5.

Next, a resin compact 3 with such lead frames 1 each embedded therein asa substrate was formed. It is to be noted that each step may be carriedout as an assembly in which a plurality of resin compacts 3 are moldedon a lead frame which is in the form of a plurality of coupled pairs oflead frames 1 until the light emitting device 10 is separated intopieces, but explanations are given with a single light emitting device10 shown in FIG. 1 for the sake of convenience.

The resin compact 3 of this example has a thermosetting epoxy resincomposition as a main component, and contains various kinds of additivessuch as white TiO₂. The resin compact 3 has a recess portion, and thelight reflecting member 1 is exposed at the bottom surface of the recessportion. On the light reflecting member 1, three light emitting elements4 including positive/negative electrodes on the upper surface and havinga rectangular shape in a plan view were placed with an Au—Sn eutectic asa bonding material 5, and bonded by passing through a reflow step and awashing step. The protective element 8 was mounted with a conductivesilver paste as the bonding member 5, and bonded by passing through acuring step.

Then, the light emitting elements 4, the protective element 8 and thelight reflecting member 1 were electrically connected using Au wires 7respectively. Thereafter, as a protective film 2, Al₂O₃ was formed in athickness of 17.5 nm by using an atomic layer deposition method. Next,the inside of the recess portion of the resin compact 3 was filled witha light transmissive dimethyl silicone resin as a sealing member 6, andthe resin was heated and cured. Thereafter, the lead frame was cut intopieces to obtain to singulate the light emitting devices 10.

Experiment 1

Each groups of a plurality of light emitting devices 10 thus producedwere stored for test at 100° C. for 168 hours in a gas which at leastcontains S₈ with an amount of about 12 ppm.

FIG. 5 shows enlarged pictures of the recess portion and itsneighborhood in the light emitting device after the test. For eachexample and comparative example, two pictures of the light emittingdevice are shown as A and B.

As is apparent from FIG. 5, in both the light emitting devices ofExamples 1 and 2, sulfuration slightly occurred to cause discolorationnear the boundary between the resin compact and the light reflectingmember, but sulfuration hardly expanded toward the center of the recessportion. In the vicinity of the light emitting element 4, sulfurationhardly occurred although slight discoloration was observed. However, inthe light emitting devices of Comparative Examples 1, 2 and 3,sulfuration and discoloration occurred extensively at the boundarybetween the resin compact 3 and the light reflecting member 1 and in thevicinity of the light emitting element 4.

Experiment 2

A plurality of light emitting devices 10 substantially similar to thosein Experiment 1 were produced except that a YAG phosphor was included inthe sealing member 6 to provide the light emitting devices 10 capable ofemitting white light, and the light emitting devices 10 thus producedwere each stored at 100° C. for 672 hours in a gas containing at leastS₈ in an amount of about 12 ppm.

FIG. 6 shows results of measurement of a luminous flux before the test,a luminous flux after the test, and a ratio of luminous flux betweenbefore and after the test (luminous flux retention rate). Sulfurationand discoloration are reduced as the luminous flux retention rateincreases.

The light emitting devices 10 of Examples 1 and 2 had the luminous fluxretention rate of about 77 to 80%. Disconnection of the wire 7 did notoccur. On the other hand, in both the light emitting devices ofComparative Examples 1 and 2, breakage of the wire occurred due tosulfuration, so that light was no longer emitted. In Comparative Example3, disconnection of the wires 7 was experienced in several lightemitting devices, and the light emitting devices in which did notexperience disconnection of the wires 7 had the luminous flux retentionrate of only about 53%. In the light emitting device of ComparativeExample 4, disconnection of wires did not occur, but the luminous fluxretention rate was only about 50%. The light emitting devices ofComparative Examples 3 and 4 had a lower luminous flux retention rate ascompared to Examples 1 and 2.

It is to be understood that although the present invention has beendescribed with regard to preferred embodiments thereof, various otherembodiments and variants may occur to those skilled in the art, whichare within the scope and spirit of the invention, and such otherembodiments and variants are intended to be covered by the followingclaims.

What is claimed is:
 1. A light emitting device comprising: a lightemitting element; a light reflecting member comprising an Ag-containinglayer disposed at a top side of the light reflecting member, such thatan upper surface of the Ag-containing layer constitutes an uppermostsurface of the light reflecting member; a resin compact formed over thelight reflecting member, wherein the resin compact defines a recess; aprotective film having a thickness of 1 nm to 300 nm and covering, in acontinuous manner, a surface of the resin compact, a surface of thelight reflecting member, and a surface of the light emitting element;and a sealing member that fills the recess and covers the protectivefilm, wherein the Ag-containing layer has a thickness in a range of 0.1μm to 0.5 μm.
 2. The light emitting device according to claim 1, furthercomprising a wire connecting the light emitting element and the lightreflecting member, wherein a material of the wire is Ag or an Ag alloy.3. The light emitting device according to claim 1, further comprising awire connecting the light emitting element and the light reflectingmember, wherein the protective film further covers, in a continuousmanner, a surface of the wire.
 4. The light emitting device according toclaim 1, wherein the Ag-containing layer contains a brightening agent.5. The light emitting device according to claim 1, wherein an amount ofAg in the Ag-containing layer is in a range of 70-99%.
 6. The lightemitting device according to claim 1, wherein the light emitting elementis bonded to the light reflecting member.
 7. The light emitting deviceaccording to claim 6, wherein the light emitting element is bonded tothe light reflecting member via a bonding member.
 8. The light emittingdevice according to claim 7, wherein the bonding member comprises amaterial selected from the group consisting of a conductive paste madeof silver, gold, or palladium; or a eutectic solder material made ofAu—Sn, or Sn—Ag—Cu.
 9. The light emitting device according to claim 6,further comprising at least one additional light emitting element thatis bonded to the light reflecting member.
 10. The light emitting deviceaccording to claim 1, wherein a thickness of the protective film is in arange of 5 nm to 100 nm.
 11. A light emitting device comprising: a lightemitting element; a light reflecting member comprising an Ag-containinglayer disposed at a top side of the light reflecting member, such thatan upper surface of the Ag-containing layer constitutes an uppermostsurface of the light reflecting member; a resin compact formed over thelight reflecting member, wherein the resin compact defines a recess; aprotective film formed by using an atomic layer deposition method, theprotective film covering, in a continuous manner, a surface of the resincompact, a surface of the light reflecting member, and a surface of thelight emitting element; and a sealing member that fills the recess andcovers the protective film, wherein the Ag-containing layer has athickness in a range of 0.1 μm to 0.5 μm.
 12. The light emitting deviceaccording to claim 11, further comprising a wire connecting the lightemitting element and the light reflecting member, wherein a material ofthe wire is Ag or an Ag alloy.
 13. The light emitting device accordingto claim 11, further comprising a wire connecting the light emittingelement and the light reflecting member, wherein the protective filmfurther covers, in a continuous manner, a surface of the wire.
 14. Thelight emitting device according to claim 11, wherein the protective filmhas a thickness of approximately 1 nm to 300 nm.
 15. The light emittingdevice according to claim 11, wherein the Ag-containing layer contains abrightening agent.
 16. The light emitting device according to claim 11,wherein an amount of Ag in the Ag-containing layer is in a range of70-99%.
 17. The light emitting device according to claim 11, wherein thelight emitting element is bonded to the light reflecting member.
 18. Thelight emitting device according to claim 17, wherein the light emittingelement is bonded to the light reflecting member via a bonding member.19. The light emitting device according to claim 17, further comprisingat least one additional light emitting element that is bonded to thelight reflecting member.
 20. The light emitting device according toclaim 11, wherein a thickness of the protective film is in a range of 5nm to 100 nm.